No abstract

No abstract

On April 4, 1968, surface air particulates were collected on cellulose fiber filters simultaneously at twenty‐two different locations throughout the Chicago metropolitan area. A 1‐cm2 portion of each filter was irradiated with thermal neutrons in Argonne National Laboratory's CP‐5 research reactor. The neutron‐induced nuclides were analyzed by γ‐ray spectrometry with 10.2 cm × 10.2 cm (4 in. × 4 in.) and 7.6 cm × 7.6 cm (3 in. × 3 in.) cylindrical NaI(Tl) crystals and a 400‐channel analyzer. By varying the neutron flux and the time of irradiation, we were able to detect by purely instrumental means twenty trace elements in surface air. The following elements, listed in decreasing order of concentration, were present: iron, chlorine, aluminum, zinc, manganese, sodium, bromine, vanadium, chromium, antimony, mercury, selenium, cerium, silver, cobalt, lanthanum, scandium, cesium, and europium. The average concentrations varied from 2400 to 0.12 ng/m3 air. Calcium concentrations in air were not quantitated.

The existence of a spring maximum in fallout deposition due to the disruption of the tropopause in middle latitudes has been debated for the past several years. Evidence obtained from air filters indicates elevated levels of radioactivity from nuclear tests in surface air during April through July 1960.

No abstract